1. Field of Invention
This invention relates to a drywall tool, specifically to use on drywall, sheet rock and cement board where a flat smooth even joint is required. More specifically it relates to a hand tool and method for spreading drywall compound or plaster and leaving a fixed height and width of plaster over a joint between two sections of drywall.
2. Description of Prior Art
Difficulty of obtaining a smooth flat uniform surface between the joints and butt ends of drywall boards, gypsum boards, sheet rock boards, cement boards & other construction boards is well known in the industry. All of these and similar boards are described herein as “drywall boards” for the purposes of these specifications. A reliable and easy method along with a tool to spread the drywall compound, cement, grout, plaster, etc, to obtain this flat surface has been the search of the construction industry for a long time. All of these compounds and similar compounds are described herein as “joint compound” for the purposes of this specification.
In an ideal situation and in skilled hands with experience a worker, one could spread joint compound properly over a drywall board joint and obtain, in most cases, a very flat and acceptable joint. The problem in industry today is that the ideal conditions and the skilled workers are a variable today especially in the rapidly expanding housing and commercial industries. By ideal conditions one would want the drywall boards to be nailed or screwed flat to the studs so that each section of board is at the same level as the board next to it which would allow for a uniform thickness of joint compound to be applied. In most construction applications, these ideal conditions do not which always occur causing the joint surface to have valleys and hills that makes creating a constant depth of joint compound become difficult. This creates a challenge to the worker to obtain a smooth and flat surface because the two drywall board surfaces are at two different heights. Usually to compensate for this problem a skilled worker knows to apply several thin layers of joint compound. This method requires a lot of time to complete because each layer of joint compound must dry before the next layer can be applied. It is common to have at least 3 layers and sometimes more to build up the level of compound to obtain a nice flat surface. One of the most commonly used joint compounds requires the worker to wait 24 hours after the first coat is applied before the next before adding an additional coat, according to it's directions. Therefore three coats could take as long as three days or longer just to build up the surface of one joint. Care must be taken not to allow each layer to be too thick since it is common that the joint compound could crack presenting additional difficulties to obtain a smooth flat surface.
The other item effecting ideal joint preparation is spreading the joint compound over a butt end joint. Butt end joints are not recessed and are at the actual height of the wall board. Applying the tape automatically brings the height of the joint higher than that of the surface of the drywall board. This requires many layers of joint compound to be applied at different widths for each application. It is not unusual to sand the joint surface between each layer to help obtain a flat surface. Sanding the joint creates a lot of fine dust creating an unhealthy environment and possibly a hazardous situation. The worker is required to wear a mask to guard against this dust entering their lungs and of course this process takes additional time above and beyond that of the compound drying time and the time to apply the next coat. Any process that reduces sanding in itself has many benefits.
As mentioned before many events can affect the ideal conditions heeded to obtain smooth flat joints. Even when the conditions are not ideal, a very skilled worker with a lot of experience in most cases can produce a very flat surface. It may require extra days of applying thin layers of compound or extra sanding but these workers will usually get the correct result Their skills are more art than science in obtaining a flat surface. The real problem in the industry is that most workers preparing joints on drywall surfaces do not have this dexterity of hand coordination to obtain good uniform flat joints when ideal conditions are not met and sometimes even when ideal conditions are present.
The industry has been in search of a tool and method to turn the art of getting a flat smooth drywall joint from an art to more of a science. A tool where a semi-skilled or even unskilled worker can get a flat smooth joint under any conditions. The following examples illustrate some known hand tools that attempt to accomplish this task; U.S. Pat. No. 2,800,672 to Gilyan (1957) discloses a tool for plastering joints. This is a combination tool which includes a straight edge blade and a curved blade. The idea is that the curved blade can be used first over the joint and then the straight edge can be used to feather the joint by adding another layer of joint compound. It is known in the industry that a curved blade does not result in a good smooth & flat joint. Usually a curved blade allows for an excessive amount of joint compound and cracking of the compound can occur during curing. In addition such a wide curve requires a steady hand to stay within the recess joints of two boards. If a worker allows the curve blade to leave the recessed area, it creates more difficulty to obtain a smooth joint. This usually requires a lot of sanding to level the high spot.
U.S. Pat. No. 2,934,936 to Vernon (1960) discloses various tools call taping trowels. One tool in particular again utilizes the curved blade concept. Actually two different curves on each side of the hand trowel. The concept is to apply an inner coat using the first smaller width, larger radius curve to to fill the joint with joint compound and after curing use the other side which has a wider width, smaller diameter curve to apply the next outer joint. Again this has similar problems as the prior patent and is not used in current techniques.
U.S. Pat. No. 3,878,581 to Perna (1974) is a variety of finishing tools for wallboard surfaces. In particular is one tool that is made up of several rigid & non-flexible plates with a laminated elastomeric blade of rubber or composite. This again has a curved blade concept as part of this combination tool and would have similar problems as the other two patents mentioned above.
U.S. Pat. No. 4,654,919 to Liberman (1987) discloses a spreader tool to apply plaster to wallboard. This tool is different than the above mentioned tools in the fact that the blade edge is flat like a normal trowel and is not cut as a curve. Instead the blade is bent into a curve position thus allowing for a worker to apply a “curved” layer as the trowel is angled and after curing, the edges of the curved compound joint could be feathered smooth using the straight edge of the blade. Actually this would be a harder to use product than the first three patents mentioned because as the tool is angled to obtain the curve, if the angle of the tool changes, the thickness of the curve would also change. The industry has determined that a curved first coat does not lead to a better joint. In most cases it creates more problems.
Finally U.S. Pat. No. 6,606,758 B1 to Fridman (2003) discloses a serrated tool for plaster over a surface joint. This products uses a trowel that has two sets of serrated edges on both of the blade ends and a cut out notch with straight edges of 3 to 4 inches. This tool, to get good results, is to be held at a 35 to 45 degree angle when using it to cover the tape. The tool when spreading compound would create a squared extrude area in the center and smaller extruded triangle rows of joint compound at the serrated edges. The tool being large would require a steady hand while covering a wide area. The serrated edges will build up joint compound on the flat part of the drywall board, only requiring more joint compound to be applied to smooth those edges This requires much more finishing sanding and time for the worker.
Objects & Advantages
Accordingly, these and other known tools of prior art fail to address the main problem of obtaining smooth flat joints using a simple method to overcome the skill required of a worker and when ideal conditions are not met. Therefore the need for a simple low cost tool and method to obtain flat, even joints of drywall is desired in the industry and has not been solved. This is why today you still see a flat edge trowel being used in the industry instead of any of the other inventions mentioned.
The invention I detail has several objects and advantages;    (a) very low cost available in a polymer or steel construction    (b) a tool that is simple to use even with an unskilled worker or a do-it-yourself homeowner    (c) a tool that uses a smallest amount of joint compound to obtain the proper joint and requires only the smallest amount of sanding in the final process.    (d) a tool that can be utilized when drywall board is applied with uneven surfaces and on butt joints and still obtain a smooth flat joint surface    (e) a tool to speed up the finished surface preparation from several days to with in 48 hours or less.